Internal Gear Pump

ABSTRACT

An internal gear pump with a field replaceable idler is disclosed that may be used for sanitary applications. Access to the idler mainly requires removal of the head. Access to the seal assembly disposed at the inboard end of the pump chamber is also fast and easy as removal of the head exposes a fastener that secures the rotor to the drive shaft. Removal of this fastener enables the rotor to be removed with a standard rotor pulling tool thereby exposing the pump chamber seal assembly which may be cleaned, serviced or replaced as needed.

BACKGROUND

1. Technical Field

This disclosure relates generally to internal gear pumps. More specifically, this disclosure relates to internal gear pumps including: a field replaceable idler; a heating/cooling tube for maintaining proper pumping temperature; a seal assembly for the pump chamber that may be replaced, cleaned or serviced without removing the drive shaft; and an improved idler assembly that includes a polymeric idler, a ceramic bushing, and a dowel that are press-fit together.

2. Description of the Related Art

A positive displacement pump causes fluid to move by trapping fluid and then forcing or displacing the trapped fluid through an outlet. Positive displacement rotary pumps are pumps that move fluid using the principles of rotation. At the inlet to the pump, the rotation captures and draws the fluid into the pump chamber before trapping the fluid and passing it through the outlet. Various types of rotary pumps are available, including, but not limited to internal and external gear pumps, screw pumps, flexible vane or sliding vane pumps, liquid ring vacuum pumps, circumferential piston pumps, rotary lobe pumps, etc. While this disclosure uses internal gear pumps as primary examples, one skilled in the art will realize that the principles disclosed herein are applicable to other types of rotary pumps as well.

Among the applications for rotary positive displacement pumps are sanitary applications. These include pharmaceutical, biomedical, food, personal care, cosmetics and the like. Only a few types of rotary sanitary pumps serve these markets. One type is rotary lobe pump, which may include an external gearbox. The gearbox is used to time or position the pump rotors (or lobes) such that they rotate in correct relationship with one another within the pump chamber. The rotors are typically non-contacting but in close tolerance to each other. A variation on the rotary lobe pump is the circumferential piston pump, where the lobe-type rotors are replaced with circumferential piston-type rotors. In either case, these pumps are expensive by virtue of their complexity and extensive and robust construction requirements.

Sanitary rotary positive displacement pumps, regardless of type, share common characteristics. First, such pumps must be designed such that they can be quickly and easily disassembled for easy and thorough inspection and cleaning of the fluid pathway. Typically, the pump components are made from stainless steel to protect against contamination of the fluid and corrosion of the contact surfaces. Because the seals that isolate the pump chamber are periodically replaced, the seal structures are typically simple in design. Sanitary rotary positive displacement pumps should be able to operate at low speeds (RPMs) for gentle liquid handling and they should be able to operate at both high and low temperatures with liquids having high or low viscosities. Finally, sanitary rotary positive displacement pumps must conform to recognized sanitary standards which may vary depending upon the specific application.

Notably absent from sanitary rotary positive displacement pump types are gear pumps. This may be true because the fluid pathway of most gear pumps is not easily accessible for cleaning, even though the components of gear pumps may be fabricated from materials appropriate for sanitary use, such as stainless steel. Further, external gear pumps are unsuitable for sanitary service because the bearings, which support the two gear shafts, are usually internal to the pump and in contact with the liquid being pumped. Most bearing materials cannot come into contact with sanitary liquids. Further, the bearings are not easy to access and clean, which is necessary for a sanitary application.

In the case of an internal gear pump, the European Hygienic Engineering and Design Group (EHEDG) guidelines do not permit the idler pin of an internal gear pump to be press-fit onto its head because EHEDG guidelines do not allow for a press-fit between any two metal components disposed in a sanitary pump chamber or that come into contact with the fluid being pumped. Press-fit connections must be sealed by a gasket that is replaceable. Otherwise, the joint must be permanently welded or soldered. All of these alternatives would significantly add to the cost of an internal gear pump so it could be used in sanitary applications.

Another problem associated with the use of gear pumps for sanitary applications is the need for heating or cooling of the fluid being pumped. Normally, a gear pump is heated or cooled with either a jacket or a resistance heating system. However, in sanitary applications, the outboard end or head of the pump case must be exposed or easily accessible to satisfy sanitary regulations. As a result, traditional heating/cooling methods are rendered inefficient because of air gaps between the heating/cooling system and the head.

Thus, because of the limitations of rotary gear pumps when used in sanitary applications or applications where purity is important, there is a need for improved rotary gear pumps, which satisfy and meet the requirements for sanitary service, such as easy and fast tear down for easy cleaning and inspection as well as the use of corrosion resistant construction materials.

SUMMARY OF THE DISCLOSURE

In one aspect, a pump is disclosed that includes a bracket having an inboard end and an outboard end. A through hole extends through the bracket between the inboard and the outboard ends. For purposes of this disclosure, the inboard end of the pump or a pump component is the end that is closest to the motor while the outboard end is directed away from the motor, towards or past the pump chamber. The outboard end of the bracket may be coupled to an inboard end of a case. The inboard end of the case may include an opening. The case may further include an open outboard end that is covered by and coupled to a head. The case and the head may define a pump chamber. The inboard end of the case may further include an annular recess that surrounds the opening and that receives a seal assembly. The pump may further include a shaft that has an inboard end and an outboard end. The shaft may pass through the through hole of the bracket. The outboard end of the shaft may pass through the seal assembly and the inboard end of the case before the outboard end of the shaft is detachably coupled to a rotor. The rotor may be received in the pump chamber. The head may be sealably and detachably coupled to a dowel. The dowel may be coaxially received in and coupled to an idler. The idler may also be disposed in the pump chamber. As a result, removal of the head provides access to the idler and removal of the rotor from the shaft provides access to the seal assembly through the open outboard end of the case and removal of the head from the case.

In another aspect, a pump is disclosed that also includes a bracket having an inboard end and an outboard end as well as a through hole that extends between the inboard and outboard ends of the bracket. The outboard end of the bracket may be coupled to an inboard end of the case. The inboard end of the case may include an opening. The case may further include an open outboard end that is covered by and coupled to a head. The case and head may define a pump chamber. The inboard end of the case may further include a recess that surrounds the opening and that receives a seal assembly. The pump may further include a shaft having an inboard end and outboard end. The shaft may pass through the through hole of the bracket with the outboard end of the shaft passing through the seal assembly and the inboard end of the case before being detachably coupled to a rotor. The rotor may be received in the pump chamber. At least one of the case and/or the bracket may include a peripheral channel that accommodates a tube that extends about a central axis of the through hole, shaft and seal assembly. The tube may be in communication with a supply of heat transfer fluid for either heating or cooling the pump. The pump may further include a dowel that is coaxially received and coupled to an idler that may be disposed in the pump chamber. Removal of the head and rotor may provide access to the seal assembly through the open outboard end of the case. Further, the dowel may include an inboard end disposed axially within the idler and an outboard end that is received within a recess disposed in the head. The outboard end of the dowel may be detachably coupled to the head by a fastener. The pump may further include a seal disposed between the dowel and the head that isolates the fastener from the pump chamber.

In yet another aspect, another pump is disclosed that also includes a bracket having an inboard end and an outboard end and a through hole extending between the inboard and outboard ends. The outboard end of the bracket may be coupled to an inboard end of a case. The inboard end of the case may include an opening. The case may further include an open outboard end that is covered by and coupled to a head. The case and head may define a pump chamber. The inboard end of the case may further include an annular recess that surrounds the opening and that receives a seal assembly. The pump may further include a shaft with an inboard end and an outboard end. The shaft may pass through the through hole of the bracket. The outboard end of the shaft may pass through the seal assembly and the inboard end of the case before being detachably coupled to a rotor. The rotor may be received in the pump chamber. A dowel may be coaxially received in and press-fitted into a polymeric idler with a ceramic bushing annularly disposed between the dowel and the idler. The idler may be disposed in the pump chamber. Removal of the head and the rotor may provide access to the seal assembly through the open outboard end of the case. The dowel may further include an inboard end disposed axially within the idler and an outboard end that is received within a recess disposed in the head. The outboard end of the dowel may be detachably coupled to the head by a fastener. The pump may further include a seal disposed between the dowel and the head that isolates the fastener from the pump chamber.

In any one or more of the embodiments described above, the fastener may pass through the head.

In any one or more of the embodiments described above, the seal disposed between the dowel and the head that isolates either the recess from the pump chamber or the fastener from the pump chamber may be an o-ring.

In any one or more of the embodiments described above, the dowel may be coupled to the idler by a bushing and wherein the idler, bushing and dowel can be removed from the pump chamber and from the head by detaching the fastener from the head.

In any one or more of the embodiments described above, the outboard end of the dowel has an outboard diameter and the inboard end of the dowel has an inboard diameter that is larger than the outboard diameter and the dowel may also include a shoulder disposed between the inboard and outboard ends of the dowel. The pump may further include a seal sandwiched between the idler and the shoulder. In a further refinement of this concept, a fastener may be used to secure the dowel to the head wherein the fastener is coaxial with the dowel and the recess in the head. In still yet a further refinement, the seal may be disposed between the idler, the bushing and the shoulder.

In yet a further refinement, the head may further include a slot that encircles the recess in the head that receives the outboard end of the dowel. The seal may be disposed in the slot.

In any one or more of the embodiments described above, a bushing may be disposed between the idler and the dowel and the bushing may be press-fit onto the dowel and the idler may be press-fit onto the bushing.

In any one or more of the embodiments described above, the idler may be polymeric. While a variety of polymers may be employed, one suitable polymer is polyoxymethylene.

In any one or more of the embodiments described above, the bushing may be ceramic. While a variety of ceramic materials may be utilized, carbon graphite and silicon carbide are two such ceramic materials that are suitable for use for the bushing.

In any one or more of the embodiments described above, the pump further includes a tube that extends between the case and the bracket and about the axis of the shaft. The tube may be in communication with the source of heat transfer fluid.

Other advantages and features will be apparent from the following detailed description when read in conjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the disclosed methods and apparatuses, reference should not be made to the embodiment illustrated in greater detail on the accompanying drawings, wherein:

FIG. 1 is a perspective view of a disclosed pump.

FIG. 2 is a side plan view of the pump shown in FIG. 1.

FIG. 3 is an end view of the pump shown in FIGS. 1-2.

FIG. 4 is a sectional view taken substantially along line 4-4 of FIG. 2.

FIG. 5 is a partial sectional view taken substantially along the line 5-5 of FIG. 3.

FIG. 6 is an enlarged view of the seal assembly shown in FIGS. 4-5.

FIG. 7 is an enlarged partial sectional view of the head, fastener, dowel, bushing and idler of the pump as shown in FIG. 4.

It should be understood that the drawings are not necessarily to scale and that the disclosed embodiments are sometimes illustrated diagrammatically and in partial views. In certain instances, details which are not necessary for an understanding of the disclosed methods and apparatuses or which render other details difficult to perceive may have been omitted. It should be understood, of course, that this disclosure is not limited to the particular embodiments illustrated herein.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

In FIG. 1, a pump 10 is disclosed that includes a bracket 11 that may be coupled to a case 12. As also shown in FIG. 2, the bracket 11 includes an inboard end 13 and an outboard end 14. Further, the case 12 also may include an inboard end 15 and an open outboard end 16 that may be coupled to a head 17. The head 17 may be sandwiched between the open outboard end 16 of the case 12 in a cover 18. The case 12 may further include inlet and outlet ports 21, 22. Referring to FIGS. 1-3 together, a tube 23 may encircle a central axis of the pump 10 between the case 12 and the bracket 11. As discussed in greater detail below and shown schematically in FIG. 3, the tube 23 may be in communication with a fluid reservoir 24 which, in turn, may be in communication with a pump 25 that is also in communication with the tube 23. The tube 23 may carry heat transfer fluid around the pump for purposes of maintaining a proper temperature for pumping. The cover 18 may be coupled to the case 12 and head 17 by one or more fasteners 26 that extend through the cover 18, head 17 and into the case 12 as shown in FIG. 4. Further, the cover 18, head 17 and case 12 may be secured to the brackets with a plurality of studs 27 that extend through the cover 18, the head 17, the case 12 and into the outboard end 14 of the bracket 11 as shown in the sectional view of FIG. 5.

Turning to FIG. 4, a sectional view of the pump 10 is shown that illustrates a through hole 28 that extends through the bracket 11 and that may accommodate a drive shaft 31 that also has an inboard end 32 that may be coupled to a motor (not shown) and outboard end 33 that may be coupled to a rotor 34. The shaft 31 may pass through bearing assembly 35 that may include a bearing housing 36, bearings 37, both of which may be held in place in the inboard end 13 of the bracket 11 by a locknut 38. The inboard end 13 of the bracket 11 may include and opening or enlargement of the through hole 28 as well as a recess 41 for accommodating the bearing assembly 35. While the bearing assembly 35 supports the inboard end 32 of the shaft 31, an additional bearing assembly 41 may support the outboard end 33 of the shaft 31 and may be accommodated in a recess 42 disposed in the outboard end 14 of the bracket 11 as shown in FIG. 4.

FIG. 4 also illustrates the cooling/heating tube 23, which is in close proximity to the bearing assembly 41 and the seal assembly 43. The seal assembly 43 isolates the bearing assembly 41 from the pump chamber 45 that is defined by the case 12 and head 17. The pump chamber may accommodate the rotor 34 as well as the idler 46. The idler 46 may be coupled to the head 17 by a fastener 47 and a dowel 48. The idler 46 slides over the dowel 48 and bushing 51 as shown in FIG. 7. To isolate the fastener 47 from the pump chamber, a seal 52 may be disposed between the dowel 48 and head 17 as shown in FIG. 7. More specifically, the dowel 48 may include a wider inboard end 53 and a narrower outboard end 54 that is received within a recess 55 disposed in the head 17 as shown in FIG. 7. The seal 52 may isolate the recess 55, fastener 47, and anti-rotation pin 56 from the pump chamber 45.

The seal assembly 43 is illustrated in greater detail in FIG. 6. The seal assembly 43 is secured to the case 12 by a fastener 58 and an anti-rotation washer 59. A shim 61 may be employed to provide the correct amount of pressure between the seal element 62 and the washer 63 disposed within a recess 64 that is disposed in the inboard end 65 of the rotor 34. Because the seal assembly 43 is secured to the case 12, removal of the cover 18 and head 17 followed by detachment of the rotor 34 from the outboard end 33 of the shaft 31 provides easy access to the seal assembly 43 for cleaning, servicing, removal and/or replacement.

As shown in FIG. 5 the rotor 34 is detachably connected to the shaft 31 or, more specifically, the outboard end 33 of the shaft 31 by the fastener 67. The fastener 67 is exposed by removing the cover 18 and head 17 because the head 17 is coupled to the idler 46 by way of the fastener 47, dowel 48, and bushing 51. Thus, because the idler 46 may be easily removed from the head 17, replacement of the idler 46 is a fast and easy maintenance task. Similarly, because removal of the cover 18, head 17 and idler 46 exposes the fastener 67 that secures the rotor 34 to the shaft 31, the rotor 34 may be easily removed from the pump chamber 45 using a simple tool after the fastener 67 has been decoupled from the shaft 31 and the rotor 34.

Thus, the pump 10 includes important improvements in terms of maintenance and service. The rotor 34 is easily exposed by removing the cover 18 and head 17 as the idler 46 is removed from the pump chamber 45 when the head 17 is removed. This exposes the fastener 67 and the plate 71, which secure the rotor 34 to the shaft 31. Removal of the fastener 67 enables an easy removal of the rotor 34 which exposes the seal assembly 43 for service, maintenance or replacement. With the rotor 34 removed, the entire pump chamber 45 may be easily cleaned and/or sanitized.

The idler 46 may be fabricated from a polymeric material. One suitable material is polyoxymethylene, also known as acetal, polyacetal and polyformaldehyde. Other suitable thermoplastic materials for use in such precision parts are available as will be apparent to those skilled in the art. A bushing 51 may be disposed between the dowel 48 and the idler 46. The bushing 51 may be made from a ceramic material, with two possibilities being carbon graphite and silicon carbide. Other suitable ceramic materials for a bushing disposed between a polymeric idler 46 and a metallic dowel 47 will be apparent to those skilled in the art.

Finally, returning to FIG. 5, the fastener 67 that secures the shaft 31 to the rotor 34 passes through a washer or plate 71. A seal 72 may be disposed between the plate 71 and the rotor 34 and an additional seal 73 may be disposed between the fastener 67 and the plate 71 to further ensure that contaminants cannot migrate in an outboard direction and enter the pump chamber 45.

INDUSTRIAL APPLICABILITY

An improved internal gear pump is disclosed that is suitable for sanitary applications and/or applications were purity of the pumped product is important. As opposed to prior art pumps which require removal of the drive shaft to replace the seal assembly that seals the pump chamber from the bearing assembly that supports the drive shaft, the seal assembly of the disclosed pump may be serviced, cleaned and/or replaced with very few steps. The cover and head plate are removed. Removal of the head plate also results in removal of the idler as the idler is detachably secured to the head. With the idler removed, a fastener that detachably secures the rotor to the outboard end of the shaft is exposed. Removal of this fastener enables the rotor to be removed from the pump chamber with the use of a conventional rotor pulling tool. With the rotor removed, the seal assembly is exposed and the entire pump chamber and seal assembly may be cleaned. Further, the seal assembly may be removed or serviced. Reassembly of the pump is also fast and easy as the rotor is secured back on to the outboard end of the shaft with the fastener.

The idler may also be easily replaced as the idler is secured to the head with a single fastener. The idler may be a polymeric material that may be press-fitted on to a dowel with a bushing disposed therebetween. A single fastener may be used to secure the idler to the head. Rotation of the dowel may be prevented with a pin.

Thus, an internal gear pump with separate shaft and rotor elements is disclosed. Because the shaft does not need to be removed to service the seal assembly that seals the inboard end of the pump chamber from the bearings, the seal assembly may be serviced without the need to reset the pump end clearance. Thus, the seal assembly of the disclosed internal gear pump may be replaced from the outboard end or head end of the pump with minimal disassembly. The disclosed internal gear pump does not require resetting the end clearance after replacement or servicing of the seal and/or cleaning behind the rotor. Thus, the pump may be cleaned and maintained without risk to the operating efficiency of the pump. Specifically, resetting the end clearance of an internal gear pump requires skill and time. If the end clearance is not set correctly, the pump can be damaged or operate less efficiently.

Further, the disclosed internal gear pump is a positive displacement pump equipped with a field replaceable idler that meets the EHEDG criteria because the seal is disposed between the idler and the head thereby isolating the fastener that secures the idler to the head from the pump chamber. The disclosed pump also has an effective heating and cooling system with a tube that extends about the axis of the shaft between the bracket and case for maintaining the shaft support bearing assembly and the pump chamber seal assembly at the proper pumping temperature.

While only certain embodiments have been set forth, alternatives and modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit and scope of this disclosure and the appended claims. 

What is claimed:
 1. A pump comprising: a bracket including an inboard end, an outboard end and a through hole extending between the inboard and outboard ends; the outboard end of the bracket being coupled to an inboard end of a case, the inboard end of the case including an opening, the case further including an open outboard end that is covered by and coupled to a head, the case and head defining a pump chamber, the inboard end of the case further including an annular recess that surrounds the opening and that receives a seal assembly; a shaft including an inboard end and an outboard end, the shaft passing through the through hole of the bracket, the outboard end of the shaft passing through the seal assembly and the inboard end of the case before being detachably coupled to a rotor, the rotor being received in the pump chamber; the head being sealably and detachably coupled to a dowel, the dowel being coaxially received in and coupled to an idler that is disposed in the pump chamber; whereby removal of the head and rotor providing access to the seal assembly through the open outboard end of the case and removal of the head providing access to the idler.
 2. The pump of claim 1 wherein the dowel includes an inboard end disposed axially within the idler and an outboard end that is coupled to the head with a fastener, the pump further comprising a seal disposed between the dowel and the head that isolates the fastener from the pump chamber.
 3. The pump of claim 2 wherein the fastener passes through the head.
 4. The pump of claim 1 wherein the dowel includes an inboard end disposed within the idler and an outboard end that is received within a recess disposed within the head, the pump further comprising a seal disposed between the dowel and the head that isolates the recess from the pump chamber.
 5. The pump of claim 2 wherein the seal is an o-ring.
 6. The pump of claim 4 wherein the seal is an o-ring.
 7. The pump of claim 2 wherein the dowel is coupled to the idler by a bushing, and wherein the idler, bushing and dowel can be removed from the pump chamber and from the head by detaching the fastener from the head.
 8. The pump of claim 4 wherein the outboard end of the dowel has an outboard diameter and the inboard end of the dowel has an inboard diameter that is larger than the outboard diameter with a shoulder disposed between the inboard and outboard ends of the dowel, and wherein the seal is sandwiched between the idler and the shoulder.
 9. The pump of claim 7 wherein the outboard end of the dowel has an outboard diameter and the inboard end of the dowel has an inboard diameter that is larger than the outboard diameter with a shoulder disposed between the inboard and outboard ends of the dowel, the outboard end of the dowel being disposed within a recess disposed in the head, the fastener being coaxial with the dowel and the recess, and wherein the seal is disposed between the idler, the bushing and the shoulder.
 10. The pump of claim 1 wherein the dowel includes an outboard end having an outboard diameter and an inboard end having an inboard diameter that is larger than the outboard diameter with a shoulder disposed between the inboard and outboard ends of the dowel, the outboard end of the dowel being disposed within a recess disposed in an inboard side of the head, the inboard end of the head further including a slot that encircles the recess; the pump further comprising a seal disposed in the slot that isolates the outboard end of the dowel from the pump chamber.
 11. The pump of claim 2 further including a bushing disposed between the idler and the dowel, and the bushing being press-fit onto the dowel and the idler being press-fit onto the bushing.
 12. The pump of claim 10 wherein the idler is polymeric.
 13. The pump of claim 11 wherein the bushing is ceramic.
 14. The pump of claim 1 further comprising a tube that extends between the case and the bracket and about an axis of the shaft; and wherein the tube is in communication with a source of heat transfer fluid.
 15. A pump comprising: a bracket including an inboard end, an outboard end and a through hole extending between the inboard and outboard ends; the outboard end of the bracket being coupled to an inboard end of a case, the inboard end of the case including an opening, the case further including an open outboard end that is covered by and coupled to a head, the case and head defining a pump chamber, the inboard end of the case further including an annular recess that surrounds the opening and that receives a seal assembly; a shaft including an inboard end and an outboard end, the shaft passing through the through hole of the bracket, the outboard end of the shaft passing through the seal assembly and the inboard end of the case before being detachably coupled to a rotor, the rotor being received in the pump chamber; at least one of the case and/or bracket including a peripheral channel that accommodates a tube that extends about a central axis of the through hole, shaft and seal assembly, the tube being in communication with a supply of heat transfer fluid; a dowel coaxially received in and coupled to an idler that is disposed in the pump chamber; removal of the head and rotor providing access to the seal assembly through the open outboard end of the case; the dowel including an inboard end disposed axially within the idler and an outboard end that is received within a recess disposed in the head, the outboard end of the dowel being detachably coupled to the head by a fastener; and the pump further comprising a seal disposed between the dowel and the head that isolates the fastener from the pump chamber.
 16. The pump of claim 15 wherein the seal is an o-ring.
 17. The pump of claim 15 wherein the dowel is coupled to the idler by a bushing; and wherein the idler, bushing and dowel can be removed from the chamber and head by detaching the fastener from the head.
 18. The pump of claim 15 wherein the outboard end of the dowel has an outboard diameter and the inboard end of the dowel has an inboard diameter that is larger than the outboard diameter with a shoulder disposed between the inboard and outboard ends of the dowel, and wherein the seal is sandwiched between the idler and the shoulder.
 19. The pump of claim 15 wherein the outboard end of the dowel has an outboard diameter and the inboard end of the dowel has an inboard diameter that is larger than the outboard diameter with a shoulder disposed between the inboard and outboard ends of the dowel, the outboard end of the dowel being disposed within a recess disposed in an inboard side of the head, the inboard side of the head further including a slot that encircles the recess; the pump further comprising a seal disposed in the slot that isolates the outboard end of the dowel from the pump chamber.
 20. A pump comprising: a bracket including an inboard end, an outboard end and a through hole extending between the inboard and outboard ends; the outboard end of the bracket being coupled to an inboard end of a case, the inboard end of the case including an opening, the case further including an open outboard end that is covered by and coupled to a head, the case and head defining a pump chamber, the inboard end of the case further including an annular recess that surrounds the opening and that receives a seal assembly; a shaft including an inboard end and an outboard end, the shaft passing through the through hole of the bracket, the outboard end of the shaft passing through the seal assembly and the inboard end of the case before being detachably coupled to a rotor, the rotor being received in the pump chamber; a dowel coaxially received in and press fitted into a polymeric idler with a ceramic bushing annularly disposed between the dowel and idler, the idler being disposed in the pump chamber; removal of the head and rotor providing access to the seal assembly through the open outboard end of the case; the dowel including an inboard end disposed axially and within the idler and an outboard end that is received within a recess disposed in the head, the outboard end of the dowel being detachably coupled to the head by a fastener; and the pump further comprising a seal disposed between the dowel and the head that isolates the fastener from the pump chamber. 